code: def test_unfilled(self, x, y):
      p = Plot(x, y).add(Bars(fill=False, edgecolor="C4")).plot()
      ax = p._figure.axes[0]
      fcs = ax.collections[0].get_facecolors()
      ecs = ax.collections[0].get_edgecolors()
      colors = p._theme["axes.prop_cycle"].by_key()["color"]
      assert_array_equal(fcs, to_rgba_array([colors[0]] * len(x), 0))
      assert_array_equal(ecs, to_rgba_array([colors[4]] * len(x), 1))
  
imports: import numpy
  import pandas
  from matplotlib.colors import to_rgba, to_rgba_array
  import pytest
  from numpy.testing import assert_array_equal
  from seaborn._core.plot import Plot
  from seaborn._marks.bar import Bar, Bars
label_desc: Use image node_id 10 for calling the TestBars obj's underlying member method code with example usage: obj.test_unfilled(x, y) without return types